Lens arrangements

ABSTRACT

There is disclosed a lens arrangement comprising: an input negative macro-lens array negative macro-lens aray; an output negative macro-lens aray disposed with its lenses arranged correspondingly to those of the input array, and between said input and output arrays a double convex microlens array.

FIELD OF THE INVENTION

This invention relates to lens arrangements, more particularly forforming three-dimensional images.

BACKGROUND OF THE INVENTION

Lens arrangements are known comprising input and output macrolenses ormacrolens arrays with intermediate so-called double-integraltransmission microlens screens. In all of these arrangements, the inputmacrolenses cast an image on to the microlens screen arrangement whichtransmits rays to the output lenses for reconstitution as a pseudoscopicimage that can be captured via a decoding screen on to a sensitisedscreen such as a photographic plate or film or an electronic arrangementsuch as a charge coupled device (CCD) screen.

In order to cast an image on to the screen, the input array lenses are,of course, positive, or convex lenses, and the output lenses are,naturally, similar.

The input and output lenses must be spaced about the equivalent of theirfocal lengths from the central microlens screen, which makes thearrangement somewhat more than two focal lengths long.

Problems arise with such lens arrangements that require more or lessexpensive measures for their solution or alleviation. One such problemis that the input lenses cast an image of the microlens screen as wellas of the image cast on that screen, and graininess in the final imagesis dependent upon the pitch of the microlens screen. Fine pitch screensare clearly desirable, but correspondingly expensive.

BRIEF SUMMARY OF THE INVENTION

The present invention provides lens arrangements which do not sufferfrom the problem of graininess yet which a re not expensive and whichincidentally have advantages in other ways over the conventionalarrangements.

The invention comprises a lens arrangement comprising:

an input negative macrolens array;

an output negative macrolens array disposed with its lenses arrayedcorrespondingly to those of the input array, and

between said input and output arrays, a double convex microlens array.

The input and output arrays may be of plano-concave lenses arranged withtheir plane faces facing each other and the double convex microlensarray having the convex microlens faces contiguous with the plane facesof the input and output arrays.

The input and output arrays may be of equal focal length--giving unitmagnification--or they may have different focal lengths and have theprincipal axes of corresponding macro lenses displaced from each otherproportionately to their distance from the principal axis of thearrangement as a whole.

With such arrangements it is possible to correct for chromatic and otheraberrations by using glass of different refractive indices anddispersion for the various elements.

Embodiments of lens arrangements according to the invention will now bedescribed with reference to the accompanying drawings, in which:

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-section of a first embodiment;

FIG. 2 is a ray tracing through one pair of input and outputmacrolenses;

FIG. 3 is a sample ray tracing from the output lens array;

FIG. 4 is a face-on-view of one arrangement of macrolenses;

FIG. 5 is a face-on-view like FIG. 4 of a second arrangement;

FIG. 6 is a face-on-view like FIG. 4 of a third arrangement;

FIG. 7 is a face-on-view like FIG. 4 of a fourth arrangement; and

FIG. 8 is a cross-section through a second embodiment.

DETAILED DESCRIPTION OF THE INVENTION

The drawings illustrate lens arrangements 11 comprising:

an input negative macrolens array 12;

an output negative macrolens array 13 disposed with its lenses 13aarranged correspondingly to those 12a of the input array 12; and

between said input and output arrays 12, 13, a double convex microlensarray 14.

The input and output arrays 12, 13 are of piano-concave lenses 12a, 13aarranged with their plane faces 12b, 13b facing each other and thedouble convex microlens array 14 having its convex microlens faces 14acontiguous with the plane faces 12b, 13b of the input and output arrays12, 13.

In the embodiment of FIGS. 1 to 7, the input and output arrays 12, 13are of equal focal lengths, that is to say, all the lenses of each array12, 13 are of the same focal length.

In a typical arrangement, the focal lengths LA of the input and outputmacrolenses are--80 mm, the macrolens apertures are 21 mm, the microlenspitch (aperture) p is 915 microns, and the distance `d` between theplane surfaces 12b, 13b of the macrolens arrays 12, 13 is 2.984 mm. Thefocal length of the microlenses is 1.865 mm giving an F number of 1.6 tocover the full image field.

A typical arrangement, again, may have its macrolenses 12a, 13a arrangedwith circular symmetry in the arrays 12, 13, as seen in FIG. 4, wherecircular aperture lenses are shown, or in FIG. 5, where hexagonalaperture lenses cover more of the total lens face area, or inrectangular array as seen in FIG. 6 (circular aperture lenses again) andFIG. 7 (square aperture lenses). Wider aperture lens arrangements,either with wider aperture macrolenses or more of them will gather morelight and more information to enhance depth perception.

With the arrangement of FIG. 1, the best focus from infinity to thechosen near point of the scene being imaged--the near focal distances,or `nfd`, the microlens pitch p is chosen as

    p=1.24a(λ/b).sup.0.5

where λ=wavelength of light (say 500 mm)

and where ##EQU1## t=thickness of the negative lenses 12a, 13a atthinnest point ##EQU2##

FIG. 2 shows ray tracings through one pair of input and outputmacrolenses 12a 13a, while FIG. 3 shows ray tracing over the wholemacrolens array. It will be noticed that the principal focus 31 issharp, but that there are also side bands 32. However, these side bandsare not troublesome to viewing because they are deflected out of theviewing area and they do not appear in any event to come to a focus.

FIG. 8 illustrates a lens arrangement like that of FIG. 1 except that itis arranged to form a reduced image. The output macrolenses 13a are ofhigher (negative) power than the input macrolenses 12a and have theirprincipal axes PA12a, PA13a displaced from each other proportionately totheir distance from the principal axis PA11 of the arrangement as awhole. The axes are displaced outwards from the main principal axis ofthe system to bend the rays towards main central axis.

Among advantages that can be derived from lens arrangements according tothe invention may be mentioned:

the arrangement is much more compact than previous arrangements usingpositive macrolenses;

focusing is a simple matter of adjustment along the principal axis;

larger microlenses can be used in the microlens array, because no imageis formed of the microlenses--this simplifies registration of themicrolenses of the double array and also enables better qualitymicrolenses to be formed;

the focal lengths of the microlenses can be selected for retaining focusfrom any distance, say 500 mm, to infinity;

the microlenses do not have to image points behind themselves, as allobject points are in front--this facilitates the development ofcorrected microlens separation and enables correct sequential fill ofthe micro image fields.

as the arrangement does not project images of the microlenses on to theimage plane, there are no interference effects in the recorded image;

construction of the lens is simplified;

lateral resolution is no longer governed by microlens pitch.

As mentioned, lens arrangements according to the invention can be usedfor the same purposes as the prior art, convex macrolens arrangements,in particular as a taking lens in a camera with the film overlain by amicrolens decoding screen or in a video arrangement in which a CCD arrayis overlain by such a screen or decoding is effected electronically.

What is claimed is:
 1. A lens arrangement comprising:an input negativemacrolens array; an output negative macrolens array disposed with itslenses arranged correspondingly to those of the input array, and betweensaid input and output arrays a double convex microlens array.
 2. A lensarrangement according to claim 1, in which the input and output arraysare of plano-concave lenses arranged with their plane faces facing eachother and the double convex microlens array has the convex microlensfaces contiguous with the plane faces of the input and output arrays. 3.A lens arrangement according to claim 2, wherein the input and outputarrays are of equal focal length.
 4. A lens arrangement according toclaim 3, wherein the lens arragement is corrected for aberrations byusing glass of different refractive indices for the various elements. 5.A lens arrangement according to claim 2, wherein the input and outputarrays have different focal lengths and have the principal axes ofcorresponding microlenses in the arrays displaced from each otherproportionately to their distance from the principal axis of thearrangement as a whole.
 6. A lens arrangement according to claim 5,wherein the lens arragement is corrected for aberrations by using glassof different refractive indices for the various elements.
 7. A lensarrangement according to claim 2, wherein the lens arragement iscorrected for aberrations by using glass of different refractive indicesfor the various elements.
 8. A lens arrangement according to claim 1, inwhich the input and output arrays are of equal focal length.
 9. A lensarrangement according to claim 8, wherein the lens arragement iscorrected for aberrations by using glass of different refractive indicesfor the various elements.
 10. A lens arrangement according to claim 1,in which the input and output arrays have different focal lengths andhave the principal axes of corresponding microlenses in the arraysdisplaced from each other proportionately to their distance from theprincipal axis of the arrangement as a whole.
 11. A lens arrangementaccording to claim 10, wherein the lens arragement is corrected foraberrations by using glass of different refractive indices for thevarious elements.
 12. A lens arrangement according to claim 1, correctedfor aberrations by using glass of different refractive indices for thevarious elements.